A radio communication system such as a mobile telephone system and a wireless MAN (Metropolitan Area Network) is widely in use today. Also, in a radio communication field, a next generation communication technology to improve communication speed and capacity is under continuous discussion.
With regard to such a radio communication system, there is LTE/EPC (Long Term Evolution/Evolved Packet Core), as an example. The LTE/EPC is standardized at the 3GPP (3rd Generation Partnership Project) as a next generation radio communication system to succeed the third generation mobile telephone network (3G Mobile System).
The LTE/EPC includes an LTE network and an EPC network as a core network. The LTE network, a radio access network conforming to the LTE standard, may also be designated as E-UTRAN (Evolved UMTS Terrestrial Radio Access Network). Further, the EPC network, which is also called as SAE (System Architecture Evolution), is connected to an IP (Internet Packet) network (or simply, a packet network) through an IMS (IP Multimedia Subsystem) network. The IP network includes an ISP (Internet Service Provider) network (or the Internet) and an intranet, for example.
In the LTE/EPC, a mobile station (mobile terminal: UE or User Equipment) may be connected to the EPC network through the LTE network, and may be connected to the IP network through the EPC network or the IMS network. By accessing a variety of server apparatuses and terminal apparatuses connected to the IP network, the mobile station may receive a variety of services, such as a browsing service by a browser, a video distribution service and VoIP (Voice over IP).
The EPC network includes a plurality of nodes, such as MME (Mobile Management Entity), S-GW (Serving Gateway), P-GW (Packet Data Network Gateway) and PCRF (Policy and Charging Rules Function). With a connection to the IMS network through the S-GW and the P-GW, the mobile station may access the IP network.
Now, in such a radio communication system, there is a technique called traffic offload. In the traffic offload, traffic from a mobile station is carried to the ISP network without passing through the S-GW and the P-GW, so that traffic in the EPC network may be reduced.
As an example of the traffic offload technique, an offload apparatus is provided in the EPC network. The offload apparatus functions as an anchor point for traffic from the mobile station (radio access network), to transfer the traffic from the mobile station to a network for offloading which is different from the EPC network. The network for offloading may be called an offload network (such as the IP network and an MPLS (Multi Protocol Label Switching) network), for example. Offloaded traffic arrives at a target IP network through the offload network.
For the offload traffic in the EPC network, for example, an offload apparatus which functions as an offload anchor point is determined for each communication channel, when the communication channel is set at the mobile station. The offload apparatus which functions as the offload anchor point is not changed if a base station connecting the mobile station is changed. In other words, the whole offload traffic from the mobile station passes through the offload apparatus, the anchor point. By this, it is possible to avoid disconnection or interruption of communication between the mobile station and the IP network caused by the movement of the mobile station.
Meanwhile, there is another technique as described below, for example. Namely, when a mobile terminal is expected to move in to a radio area, and a radio base station corresponding to that area is accommodated in another switching system, a standby connection is formed from the switching system, which accommodates the radio base station currently in communication, to a pseudo terminal which is accommodated in the other switching system. By this, route selection after handover can be made within a short time, and an effective use of a network link resource can be attained, for example.
Patent document 1: Japanese Laid-open Patent Publication No. 10-243440.
However, with regard to the above-mentioned offload technique, a phenomenon called “trombone phenomenon” may occur.
For example, there is a case as described below. Namely, with the provision of a plurality of offload apparatuses in an EPC network, an offload apparatus may be changed by the movement of a mobile station. In such a case, an offload apparatus after the change is different from the offload apparatus which originally acts as an anchor point. In such a state, offload traffic passes through the anchor point which is determined originally, despite that a transmission distance to a target IP network from the offload apparatus after the change can be greatly reduced, as compared with a transmission distance to the target IP network from the offload apparatus which acts as an anchor point. The trombone phenomenon signifies that, in spite of the movement of a mobile station, the whole offload traffic from the mobile station passes through an offload apparatus which is originally determined as an anchor point, for example.
Because extra traffic is produced between the offload apparatuses by the trombone phenomenon, the reduction of a traffic load in the core network (EPC network) may be impeded.
However, the aforementioned technique related to standby connection aims to shorten a route selection time at hand-off by the formation of a standby connection to a pseudo terminal by a switching system, for example, which does not provide any solution to the trombone phenomenon. Therefore, by the above technique, it is difficult to reduce traffic in the core network.